In view of the extended marketing channels, germs (e.g., bacteria) have to be removed from the beer in order to make it storable. Nowadays, germ removal is mainly carried out by pasteurization of the beer. To this end, the beer is, for example, bottled or canned, and heated to a temperature of between 62 and 69° C. to kill the germs.
This pasteurization does, however, involve considerable energy consumption. It has the further disadvantage that the energy introduced can trigger chemical reactions which impair the product and are difficult to control. These reactions can, for example, adversely affect the flavor of the product (“pasteurized taste”), and there is also the danger that undesired substances will form. Pasteurization is, therefore, a relatively expensive germ removing method involving high energy expenditure and, consequently, having harmful effects on the environment as well as reducing the quality of the product.
Another known germ removing method is cold-filtration. Cold-filtered beer is available as so-called “draft beer” in, for example, the United States, Japan and Korea. This beer is prohibited in Europe because it contains technical enzymes.
These technical enzymes are present in the beer to counteract a drawback inherent in the cold-filtration method: early clogging of the filter. This clogging is due to deposits of substances to be filtered out of the beer on the upstream side of the filter, e.g., a membrane filter. The deposits are difficult or even impossible to remove from the filter and reduce the service life of the filter. This increases the cost of producing the beer as membrane filters are expensive.
To prolong the service life of the filter, the manufacturers of membrane filters recommend cleaning the used membranes by treating them with proteases, glucanases, and xylanases, as well as with chemicals such as surfactants, acids/bases, and oxidizing agents, to make them reusable. This cleaning can be carried out at, for example, two stages, with the above-mentioned enzymes at a first stage, followed optionally by additional cleaning with the above-mentioned chemicals in a second stage.
The literature also discloses methods of cleaning membrane filters used in filtering beer, which cleaning methods involve a variety of techniques. For example, U.S. Pat. No. 5,227,819 discloses a method for the cleaning of a polyamide microporous membrane used in cold-filtering beer by passing a dilute alkaline solution through the microporous membrane. International Patent Application WO 96/23579 discloses a somewhat different method of cleaning a membrane filter used in beer filtration. That method is characterized by treating the membrane filter with an enzyme-containing aqueous solution of β-glucanases, xylanases, and cellulases, cleaning the membrane filter with an acidic aqueous cleaning solution, and cleaning the membrane filter with a peroxide-containing alkaline cleaning solution.
Given, for example, a filter area of approximately 320 m2, a cleaning procedure will, by way of example, make provision for enzymatic cleaning after every 5,000 hectoliters filtered and an additional chemical cleaning after every 20,000 hectoliters filtered. The typical service life of filters with the above-mentioned filter area of approximately 320 m2 having undergone the manufacturer-recommended cleaning is approximately 100,000 hectoliters.
The previously known cleaning procedures do, however, have the disadvantage that they are unable to remove the deposits on the filter to a satisfactory extent, which causes the cleaning efficiency to diminish strongly as the membrane filter increases in age.
Yet another disadvantage is the sudden, random clogging of the filter membrane, unrelated to standard norms like total nitrogen content, or percent of original wort. A fully clogged membrane filter cannot be satisfactorily cleaned under procedures following the current state of technology, which greatly reduces the service life of the filter. It is difficult to determine when a filter will become so clogged that it cannot be satisfactorily cleaned, and, therefore, a filter may be cleaned prematurely or not in time, i.e., too early or too late.
In view of the foregoing problems, there exists a need for an improved method of producing beer, particularly wherein the beer can be filtered through a filtration medium that can be satisfactorily cleaned and reused. The present invention provides such a method. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.